Nematode worms hitch a ride on slugs

Slugs and other invertebrates provide essential public transport for small worms including Caenorhabditis elegans
in the search for food, as researchers from Kiel University have now
found out. These worms are around a millimeter long and commonly found
in short-lived environments, such as decomposing fruit or other rotting
plant material. Read more... The worms face a high level of unpredictability in these
environments as temperature and food availability fluctuate, and
frequently need to move to new locations. However, little is understood
on how such a small animal with limited mobility is able to travel long
distances to find new food. Research published today in the open access
journal BMC Ecology

provides new insights into the natural ecology of nematodes and shows how the animals solve this transportation problem.

Searching in gardens and compost heaps, a team of researchers collected
over 600 slugs, and over 400 other invertebrates including flies,
centipedes, spiders, beetles and locusts. Through dissection and
microscopic analysis, they tested for the presence of nematode worms
that may have been hitching a ride on those animals. The survey revealed
that nematode worms are commonly found in slugs, woodlice and
centipedes, having possibly been unintentionally taken up while these
animals feed on rotting plant material. Further experiments confirmed
that the worms invaded the guts of slugs, survived and proliferated
within the intestines, and were subsequently excreted alive with the
slug feces.

Lead author Hinrich Schulenburg from Kiel University’s department of
Evolutionary Ecology and Genetics and member of the research focus “Kiel
Life Science” said: “Even though nematode worms are one of the most
intensively studied organisms in almost all biological disciplines, we
still have very little understanding of their natural ecology. Our study
reveals a previously unknown nematode lifestyle within the guts of
slugs. The worms appear to have evolved to persist in the harsh
environment of slug intestines, similar to a symbiont or even a
parasite.”

To test the worm’s ability to enter and persist in the slug’s
intestines, they performed a laboratory experiment, during which 79
slugs were exposed to a total of 1,185,000 fluorescently-tagged worms,
which was followed by microscopic analysis of the dissected slugs.

The nematode worms, at various stages of their lifecycle, were able to
invade and persist for a short time in slug intestines. Through further
analysis of the slug feces, the team confirmed that the worms survived
the entire passage through the digestive system, and were subsequently
excreted alive. The nematode worms persisted for not more than one day
in the slugs’ intestines, suggesting that the worms may achieve longer
travel by repeated invasion of different slugs.

As the worms enter and leave the slug without any obvious harm and the
slugs survived large worm infestations without any obvious damage, it is
thought that this could be a harmless interaction where at least the
nematodes benefit, but further research is needed to rule out a
parasitic association.

The team suggest that the worms take advantage of the moist environment
within some invertebrates, especially snails and slugs which constantly
produce mucus to aid locomotion. Slug intestines may be even more
advantageous because they also provide a bacterial community which may
be exploited as food for the worms.

Dr. Carola Petersen, the lead scientist of the study, in front of an enormous compost heap, which has been one of the Caenorhabditis elegans collection sites.
Photo: Carola Petersen, Hinrich Schulenburg